1. Technical Field
The present invention relates to a liquid crystal display (LCD) and, more particularly, to an LCD having a feed-forward circuit capable of preventing colors from blurring on an LCD panel.
2. Related Art
In recent years, personal computers, televisions or the like have become lightweight and small-sized, which has been therefore accompanied by requirements for lightweight and small-sized displays, so that flat panel displays such as the LCD, as opposed to the cathode ray tube (CRT), are under development.
The LCD is a display in which an electric field is applied to liquid crystal having an anisotropic dielectric constant and injected between two substrates, and the intensity of the electric field is adjusted so as to adjust the amount of light transmitted onto the substrate from an external light source (backlight), thereby obtaining a desired image signal.
The LCD is representative among portable flat panel displays, and a thin film transistor liquid crystal display (TFT-LCD), which uses TFTs as switching elements, is mainly employed.
In general, the LCD includes: an LCD panel having an upper substrate, a lower substrate, and a liquid crystal disposed between the upper and lower substrates; a driving circuit for driving the LCD panel; and a backlight for emitting light toward the LCD panel. The LCD is classified as either a color filter LCD or a color field sequential LCD according to the manner in which a color image is displayed.
In the color filter LCD, one pixel is divided into R, G and B sub-pixels. R, G and B color filters are arranged on the R, G and B sub-pixels, respectively. Thus, light is emitted from one backlight to the R, G and B color filters through the liquid crystal, thereby displaying a color image.
In the color field sequential LCD, a separate light source for each of the R, G and B colors is sequentially and periodically turned on, and a color signal corresponding to each pixel is applied in synchronization with the turning-on period to thereby obtain an image with full color. That is, in the color field sequential LCD, R, G and B backlights are arranged on one pixel that is not divided into R, G and B sub-pixels, unlike in the color filter LCD. Lights of three primary colors of red, green and blue are respectively emitted from the R, G and B backlights toward one pixel through the liquid crystal in a time-division manner, thereby utilizing persistence of vision to display the color image.
Accordingly, the color field sequential LCD requires only one-third of the number of pixels while maintaining the same resolution as that of the color filter LCD, so that it has advantages in that high integration can be implemented, and color reproduction equal to that of a color TV and a fast moving picture can be realized.
Unlike the color filter LCD in which a scanning operation is sequentially performed from an upper end to a lower end of a screen, the color field sequential LCD has different driving times of R, G and B backlights in each pixel to synthesize light of three primary colors of red, green and blue so that a color is displayed, and this is why one frame is divided into three subframes and is driven.
That is, one frame is divided into an R subframe displaying an R color, a G subframe displaying a G color, and a B subframe displaying a B color, so that the R backlight is driven in the R subframe to display the R color, the G backlight is driven in the G subframe to display the G color, and the B backlight is driven in the B subframe to display the B color, thereby displaying R, G and B colors per subframe emitting lights different from each other to represent a color image.
The color field sequential LCD has advantages in that a resolution about three times that in the same panel can be implemented and light efficiency can be enhanced because it does not use a color filter, in contrast to the color filter LCD. On the contrary, it has one frame divided into three subframes and driven so that it requires a driving frequency at least six times higher than that of the color filter LCD and a fast operating characteristic is required.
Liquid crystal deteriorates due to its own property when a voltage having the same polarity is continuously applied thereto, so that a voltage having the opposite polarity should be applied thereto. Accordingly, when a positive voltage is applied to any one pixel, a negative voltage should be applied to the pixel in the next frame so as to drive the pixel.
Prior LCDs have certain shortcomings. For example, an interference phenomenon between adjacent lines, that is, a color blurring, often occurs when predetermined R, G and B digital data are received in each line of the LCD panel, so that image quality and life of the LCD panel are degraded.